I have used these one way ref to adviser sets for six years now (always Sennheiser) and they are invaluable in both referee coaching and match observer roles. We have bought a set for each of our Society MOs and Referee Coaches - six years ago we got a guideline spec from RFU and bought the sets from a RFU recommend retailer.
This time around Hampshire (and rest of Southern Federation) followed RFU guidelines so we use the RFU standard sets (Sennheiser ENG SET ew-112 606-648 MHz frequency with 1xEK 100 G3 receiver; 1xSK 100 G3 body pack transmitter; ME 2 clip on mike) as ordered through and distributed by Juliet Smith at Twickenham at the start of last season to Societies & Federations, plus the four Groups. The RFU did a special 3 year lease-purchase deal (about £300 a pair and we had 12 - ouch!). The old Sennheiser ones had to go as their frequency band is now illegal - Home office sold the bands to mobile companies for 4G.
The RFU holds a central license for these new kits and frequencies as required by Wireless Telegraphy Act (see OFCOM site) - it is an offence to use such sets without a license and with non-allocated frequencies. When we bought the first Sennheiser sets I was involved also with my wife in buying loads of radios for the Pony Club and they had the same issues re licenses - so did a lot of reading up at the time.
It is important at Fed and Group level that all Match Observers and Referee Coaches have the same sets for combined listen in, when 'Shadows' are being trained, or on Consistency/Convergence/Coherence Training (all SWG assessors or all Federation or Society assessors at one match).
Also more and more clubs have bought a receiver set to link to their club's DVD camera so you get refs sound on the match DVD - these are L5 down to L9 that I have seen all over South West and London & South East Regions.
I thought all Societies were involved in the new Sennheiser's last season as RFU sent the details to us all, but in a totally separate telephone communication today (I suspect with the same AMGS :biggrin
I have learnt that D&W were not necessarily in that RFU round of kit purchase.
When I speak at conferences around Europe and in UK I mostly am given the same Sennheiser kit to use - so must be decent stuff if the pro sounds people use it.